Nitro- and amino-substituted fluorans

ABSTRACT

A chromogenic material of normally colorless form is disclosed, having the structural formula:   WHEREIN ONE OF R, R1, R2, and R3 represents nitro- or aminoradical and the remaining other of R, R1, R2, and R3 comprise hydrogen, halogen, phenyl and alkyl radicals and R4 represents alkyl radicals having less than five carbons; said material assuming a colored form upon reactive contact with a Lewis acid molecule. Examples include 6&#39;&#39;-diethylamino-2&#39;&#39;-nitrofluoran; 2&#39;&#39;amino-6&#39;&#39;-diethylaminofluoran; 6&#39;&#39;-diethylamino-3&#39;&#39;-methyl-2&#39;&#39;nitrofluoran; 2&#39;&#39;-amino-6&#39;&#39;diethylamino-3&#39;&#39;-methylfluoran; 6&#39;&#39;diethylamino-2&#39;&#39;-methyl-4&#39;&#39;-nitrofluoran; 4&#39;&#39;-amino-6&#39;&#39;-diethylamino2&#39;&#39;-methylfluoran; 2&#39;&#39;-chloro-6&#39;&#39;-diethylamino-3&#39;&#39;methyl-5nitrofluoran; and 6-amino-2&#39;&#39;-chloro-6&#39;&#39;-diethylamino-3&#39;&#39;methylfluoran.

United States Patent inventor Chao-han Lin Dayton, Ohio Appl. No. 792,279

Filed Jan. 21, 1969 Patented Nov. 30, I971 Assignee The National Cash Register Company Dayton, Ohio NITRO- AND AMINO-SUBSTITUTED FLUORANS 6 Claims, 2 Drawing Figs.

3/1970 Kimura etal, 117/361 Primary Eiaminer-Alex Mazel Assistant Examiner-Anne Marie T. Tighe Attorneys-E. Frank McKinney and Robert J. Shafer ABSTRACT: A chromogenic material of normally colorless form is disclosed having the structural formula:

wherein one of R, R,, R and R represents nitroor aminoradical and the remaining other of R, R,, R and R comprise hydrogen, halogen. phenyl and alkyl radicals and R, represents alkyl radicals having less than five carbons; said material assuming a colored form upon reactive contact with a Lewis acid molecule. Examples include 6-diethylamino-2- nitrofluoran; 2-amino-6-diethylaminofluoran; 6'- diethylamino-3'-methyl-2-nitrofluoran; 2'-amino- 6'diethylamino-3'-methylfluoran; 6'-diethylamino-2'-methyl- 4'-nitrofluoran; 4'-amino-6'-diethylamino-2'-methylfluoran; 2-chloro-6'-diethylamino-3'methyl-S-nitrofluoran; and 6- amino-2'-chloro-6'-diethylamino-3'-methylfluoran.

PAIENIEnnnvaolsn 3,624,107

f ET OF RECORD MATERIAL COATED ON THE REAR WITH MINUTE PRESSURE-RUPTURABLE CAPSULES CONTAINING LIQUID SOLUTION OF CHROMOGENIC MATERIAL DEVELOPABLE ON CONTACT WITH AN ELECTRON- ACCEPTING MATERIAL OF THE LEWIS- ACID TYPE T0 COLORED FORM RECEIVING SURFACE OF UNDERSHEET COATED WITH :2 l)ELECFp'EON-ACCEFTING MATERIAL OF THE LEWIS- I TY FIG. 2

INVENTOR CHAO -HAN LIN BY WW HIS AGENT BACKGROUND OF THE INVENTION This invention pertains to novel chromogenic compounds for use in pressure-sensitive record material and to an improved mark-forming manifold system incorporating these novel chromogenic compounds. More specifically, this invention pertains to nitroand amino-substituted dialkylamino fluorans which have the form of substantially colorless, i.e. white, or slightly colored solids, or approach being colorless when in dilute liquid solution, but which may be converted to dark-colored forms upon reactive contact with appropriate acidic material. As used in mark-forming systems, marking in desired areas on support webs or sheets may be accomplished by effecting localized reactive contact between the novel chromogenic material and the acidic material on or in such a web or sheet, such material being brought thereto by transfer, or originally there, in situ, the desired reactive contact forming relatively intensely colored materials in the intended image areas.

Pressure-sensitive, mark-forming systems of the prior art include that disclosed in application for Letters Pat. No. 392,404, filed Aug. 27, 1964, now abandoned in the names of Robert E. Miller and Paul S. Phillips, Jr. The above-mentioned patent application provides a marking system of disposing on and/or within sheet support material, mutually reactant but unreacted mark-forming components (at least one component of which is a polymeric material) and a liquid solvent in which each of the mark-forming components is soluble, said liquid solvent being present in such form that it is maintained isolated by a pressure-rupturable barrier from at least one of the mark-forming components until an application of pressure causes a breach or rupture of the barrier in the area delineated by the pressure pattern. The mark-forming components thereby are brought into reactive contact, producing a distinctive mark.

It is another object of this invention to provide compounds, based upon the nitroand amino-substituted dialkylamino fluorans disclosed herein which are substantially colorless, or slightly colored, in dilute solution or not, offering a new and improved variety of chromogenic characteristics, and yielding novel, relatively dark-colored, substances upon contact with color-activating materials.

It is a further object ofthis invention to provide new and improved, normally substantially colorless, chromogenic substances yielding Lewis acid-reacted color products which ex-;

hibit improved color stability on exposure to light and improved reproduction capabilities when copied by xerographic or diazo processes.

It is a further object of this invention to provide new and improved, normally substantially colorless, chromogenic substances yielding colored reaction products when placed in reactive contact with certain selected Lewis acid materials.

It is a further object of this invention to provide a new and improved mark-forming system which comprises disposing, within a web or upon the surface of a web or sheet support material, unreacted chromogenic material in a location suitable for subsequent reactive contact with an acidic material to produce relatively dark-colored reaction products, thus providing means for making marks of desirable color intensity and hue.

In accordance with one feature of this invention, there is provided a novel, substantially colorless or slightly colored, chromogenic compound having the structural formula:

2-amino-6'-diethylamino-3-methylfluoran having the structural formula:

6'-diethylamino-2'-methyl-4'-nitrofluoran having the structural formula:

6-amino-2-chloro-6'-diethylamino-3'-methylfluoran having.

the structural In accordance with another feature of this invention, a new composition of matter is disclosed which comprises a darkcolored product of chemical reaction having a resonant chemical structure and produced by contact of a color-activating material with one of the above-mentioned chromogenic compounds. The color-developing or activating material is an acidic substance useful for converting the chromogenic compounds to colored forms.

The method of marking of this invention, i.e., the method of developing a dark-colored material from substantially colorless or slightly colored chromogenic compounds, comprises providing a chromogenic compound selected from among the above-mentioned compounds and bringing such chromogenic compound into reactive contact with an acidic color-activating substance, in areas where marking is desired, to produce a dark-colored form of the chromogenic compound by the action thereon of said acidic substance.

Acidic materials employed in this invention can be any compound within the definition of a Lewis acid, i.e., any electron acceptor. Preferably, acidic organic polymers such as phenolic polymers are employed as the acidic material. The novel chromogenic materials exhibit the advantage of improved color stability when they are reacted with such phenolic polymers. Solution formation of solid particles of the polymeric material in a solvent system with the substantially colorless chromogenic compounds permits penetration of the dark-colored reaction product into a porous support sheet, e.g., paper, so that the colored form of the chromogenic material is absorbed into the body of the sheet and is not merely on the surface of the sheet. The absorption feature provides protection against erasure of recorded data by attrition of the surface of a record sheet made in accordance with the present invention.

BRlEF DESCRIPTION OF THE DRAWING FIG. I is a diagrammatic representation of a two-sheet unit manifold, in perspective. The bottom surface of the overlying sheet is supplied on the surface or near the surface with a multiplicity of minute pressure-rupturable microcapsules containing a solution of the novel, substantially colorless, chromogenic component. An acidic component, such as an acid clay or a phenolic polymeric material lies within the lower web or undersheet or upon the upper surface of the lower web or undersheet. A colored mark is made by the use of a stylus, a type character, or other pressure-exerting means applied to the two-sheet unit manifold.

The encapsulated solution is released on the event of rupture of the capsules in writing operations, as is shown in FIG. 2.

FIG. 2 is a sectioned view of the two-sheet unit manifold of FIG. 1. The elements are not to scale and are so-shown in order to more effectively depict their interrelation. The released solution is transferred from the overlying or basesheet to the receiving surface of the underlying sheet in conformance with the pressure pattern of the writing operation. The drawing shows that the top of the underlying sheet is coated or impregnated with a material reactant with the chromogenic material, e.g., an acid clay or an acidic phenolic polymer material; and that capsules are present on the overlying or basesheet which capsules contain a liquid solution of chromogenic material. In another embodiment of the record material, however, the capsules can contain the polymeric phenolic material in liquid solution and the receiving surface of the underlying sheet can be supplied with the chromogenic material. The improvement in the system resides in the chromogenic material, which chromogenic material is the novel substance of the instant invention.

Referring again to FIG. 1, comprising an overlying or basesheet having the chromogenic material located within or upon the sheet; it is possible to incorporate the chromogenic material in a solid, crystalline state in a binder material so that the chromogenic material may be transferred from the overlying sheet, upon the application of pressure, to deposit some of the chromogenic material on the receiving surface of the undersheet, which receiving surface carries a color-activating polymeric material. Preferably, the chromogenic substance is dissolved in an appropriate solvent and minute droplets of the solution of the chromogenic material are encapsulated in minute, rupturable, capsules. It is apparent that many other arrangements are possible, including different configurations and relationships of the solvent and all of the mark-forming materials with respect to their encapsulation and location on the supporting underlying or overlying sheets or webs can be envisioned. Such arrangements are thoroughly described in the aforementioned abandoned application Ser. No. 392,404 in the names of Miller et al. and need not be repeated herein.

SUMMARY OF THE INVENTION It is noted that the polymeric mark-forming components should have a common solubility with the novel chromogenic material in at least one liquid solvent when the acid-reacting material is a phenolic or other acidic organic polymer. It is also noted that in a single system several chromogenic materials may be used with the same or different polymeric materials. Several polymeric materials can be reactively contacted with a single chromogenic compound or with a mixture of chromogenic compounds.

As mentioned above, the solvent can be maintained in physical isolation in minute droplets until such time as it is released by application of pressure. This may be accomplished by. several known techniques, but, preferably, isolation is maintained by encapsulation of individual droplets of the solvent in a microcapsule according to the procedures described, for example, in U.S. Pat. No. 2,712,507, issued July 5, 1955 on the application of Barrett K. Green; U.S. Pat. No. 2,730,457, issued .lan. l0, 1956 on the application of Barrett K. Green and Lowell Schleicher; U.S. Pat. No. 2,800,457, issued July 23, 1957 on the application of Barrett K. Green and Lowell Schleicher; U.S. Pat. No. 2,800,458, issued July 23, 1957 on the application of Barrett K. Green, reissued as U.S. Pat. No. Re. 24,899 on Nov. 29, 1960; and U.S. Pat. No. 3,04 l ,289, issued June 26, 1962 on the application of Bernard Katchan and Robert E. Miller. The microscopic capsules, when disposed within or upon a supporting web as a multiplicity in contiguous juxtaposition, are rupturable by pressure, such as normal marking pressure found, for example, in writing or typing operations.

The material or materials chosen as the wall material for the droplet-containing microcapsules, in addition to being pressure rupturable, must be inert or unreactive with respect to the intended contents of the capsules and other mark-forming components so that the capsule wall material will remain intact under normal storage conditions until such time as it is released by an application of marking pressure. Preferred examples of eligible capsule wall materials include gelatin, gum arabic and many others thoroughly described in the aforementioned patents.

For most uses in record material, the capsule size should not exceed about 50 microns in diameter. Preferably, the capsules should be smaller than about 15 microns in diameter.

The acidic organic polymeric material useful for developing the color of novel chromogenic compounds in this invention include phenolic polymers, phenol acetylene polymers, maleic acid-rosin resins, partially or wholly hydrolyzed styrene-maleic anhydride copolymers and ethylene-maleic anhydride copolymers, 'carboxy polymethylene and wholly or partially hydrolyzed vinylmethylether-maleic anhydride copolymer and mixtures thereof.

More specifically, phenolic polymers found useful include alkyl-phenol acetylene resins, which are soluble in common organic solvents and possess permanent fusibility in the absence of being treated by cross-linking materials. Another specific group of useful phenolic polymers are members of the type commonly referred to as novolacs," (a type of phenolformaldehyde polymeric material) which are characterized by solubility in common organic solvents and which are, in the absence of cross-linking agents, permanently fusible. Resol resins, if they are still soluble, may be used, though they are subject to change in properties upon aging. Generally, phenolic polymer material found useful in practicing this invention is characterized by the presence of hydroxyl groups and by the absence of groups such as methylol, which tend to promote infusibility or cross-linking of the polymer, and, further, by being soluble in organic solvents and relatively insoluble in aqueous media. Again, it should be remembered that mixtures of these organic polymers and other acidic materials can be employed.

A laboratory method useful in the selection of suitable phenolic resins is the determination of the infrared absorption pattern. It has been found that'phenolic resins which undergo absorption in the 3,2003,500 cm. region (which is indicative of hydroxyl groups) on the resin molecules and which do not absorb in the l,600l,700 cm. region are eligible. This latter absorption region is indicative of desensitization of hydroxyl groups which desensitization renders such groups unavailable for reaction with the chromogenic materials.

The preparation of some organic polymeric materials useful for practicing this invention has been described in klndustrial and Engineering Chemistry," Volume 43, Pages 134 to 141, Jan. 195 l and a particular polymer thereof is described in example l of U.S. Pat. No. 2,052,093, issued to Herbert Honel on Aug. 25, 1936. The preparation of the phenol-acetylene polymers has been described in klndustrial and Engineering Chemistry," Volume 41, Pages 73 to 77, Jan. [949. The preparation of maleic anhydride copolymers is described in the literature, such as, for example, one of the maleic anhydride vinyl copolymers, as disclosed in Vinyl and Related Polymers, by Calvin E. Schildknecht, Second printing, published Apr. 1959, by John Wiley & Sons, incorporated: See pages 65 to 68 (styrene-maleic anhydride copolymer), 530 to 531 (ethylene-maleic anhydride copolymer), and 628 to 630 (vinylmethylether-maleic anhydride copolymer).

When the acidic material used as a mark-forming component in the present invention is one of the aforementioned organic polymers, the liquid solvent chosen must be capable of dissolving it. The solvent may be volatile or nonvolatile, and a singleor multiple-component solvent may be used which is wholly or partially volatile. Examples of volatile solvents useful in practicing the present invention include toluene, petroleum distillate, perchloroethylene, and xylene. Examples of nonvolatile solvents include high-boiling point petroleum fractions and chlorinated biphenyls. Generally, the solvent chosen should be capable of dissolving at least about 0.3 per cent, by weight, of the chromogenic material, and at least about 3 to 5 percent, by weight, of the acidic polymeric material to yield an effective reaction. However, in the preferred system, the solvent should be capable of dissolving an excess of the polymeric material, so as to provide every opportunity for utilization of the chromogenic material and, thus, to assure maximum coloration at the reaction site.

A further criterion for selection of the solvent is that the solvent must not interfere with the mark-forming reaction. In some instances, the presence of the solvent may be found to interfere with the mark-forming reaction or diminish the intensity of the mark, in which instances the solvent chosen should be sufficiently volatile to assure its removal from the reaction site soon after having brought the mark-forming components into reactive contact so that the mark-forming reaction can proceed.

Since the mark-forming reaction requires that an intimate mixture of the components be brought about through solution of said components, one or more of the mark-forming components can be dissolved in solvent droplets isolated by encapsulation, the only requirement being that at least one of the components essential to the mark-forming reaction be maintained isolated until the mark-forming reaction is desired.

In the usual case, the mark-forming components are so chosen as to produce a mark upon application of pressure to a coated system of sheets at room temperature to C.). However, the present invention also includes a system wherein the solvent component is not liquid at temperatures near room temperature but is liquid and in condition for forming solutions only at elevated temperatures.

The support sheet member on which components of the system are disposed may comprise a single or a dual sheet assembly. In the case where all components are disposed on a single sheet, the record material is referred to as a self-contained or autogenous system. Where there must be a migration of solvent, with or without the mark-forming component, from one sheet to another, the record material is referred to as a transfer" system. (Such a system may also be referred to as a two-fold" system, in that at least two sheets are required and each sheet includes a component, or components, essential to the mark-forming reaction.) Where an adequate amount of the colored reaction product is produced in liquid or dissolved from on a surface of one sheet, a colored mark can be recorded on a second sheet by transfer of the colored reaction product.

In a preferred case, where microcapsules are employed, they can be present in the sheet support material either disposed therethroughout or as a coating thereon, or both. The capsules can be applied to the sheet material as a dispersion in the liquid vehicle in which they were manufactured, or, if desired, they can be separated from the vehicle and thereafter dispersed in a solution of the acid-reacting polymeric component (for instance, 30 grams of water and 53 grams of a 1 percent, by weight, aqueous solution of polyvinylmethylether-maleic anhydride) to form a sheet-coating composition in which, because of the inertness of the solution and the capsules, both components retain their identity and physical integrity. When this composition is disposed as a film on the support material and dried, the capsules are held therein subject to release of the contained liquid by rupture of the capsule walls. The latter technique, relying on the inertness of the microcapsule and the dispersing medium of the film-forming mark-forming polymeric component, provides a method for preparing a sensitive record material coating having the capsules interspersed directly in a dry film of the polymeric material as the film is laid down from solution. A further alternative is to disperse one or more mark-forming components, and the chromogenic-material-containing microcapsules in a liquid medium not a solvent for either the mark-forming component or the microcapsules, with the result that all components of the mark-forming system may be disposed on or within the support sheet in the one operation. Of course, the several components may be applied individually. The capsules can also be coated onto a sheet as a dispersion in a solution of polymeric material which is not necessarily reactive with the capsule-contained solution of chromogenic materials.

The respective amounts of the several components can be varied according to the nature of the materials and the architecture of the record material unit desired or required. Suitable lower amounts include, in the case of the chromogenic material, about 0.005 to 0.075 pound per ream (a ream in this application meaning 500 sheets of 25inches X 38 inches paper, totaling 3,300 square feet); in the case of the solvent, about 1 to 3 pounds per ream; and in the case of the polymer, about 0.5 pounds per ream. In all instances, the upper limit is primarily a matter of economic consideration.

The slurry of capsules can be applied to a wet" web of paper, for example, as it exists on the screen of a Fourdrinier paper machine, so as to penetrate the paper web a distance depending on the freeness of the pulp and the water content of the web at the point of application. The capsules can be placed directly in or on a paper or support sheet. Not only capsule structures, but continuous films which contain a multitude of microscopic, unencapsulated, droplets for local release in an area subjected to pressure can be utilized. (See, for example, U.S. Pat. No. 2,299,694 which issued Oct. 20, 1942, on the application of Barrett K. Green.)

With respect to the acidic organic polymeric component, a solution thereof in an evaporable solvent can be introduced into an amount of water and the resulting mixture can be agitated while the evaporable solvent is blown off by an air blast. This operation leaves an aqueous colloidal dispersion slurry of the polymeric material, which may be applied to finished paper so as to leave a surface residue or the slurry may be applied to a wet web of paper or at the size press station of a paper making machine. in another method for making a polymer-sensitized sheet, the water-insoluble polymer can be ground to a desired or required particle size in a ball mill with water, preferably with a dispersing agent, such as a small quantity of sodium silicate. lfa binder material of hydrophilic properties is ground with the polymeric material, the binder itself may act as a dispersant. If desired, an amount of binder material of up to 40 percent, by weight, of the amount of polymeric material can be added to the ball-milled slurry of materials; such binder materials being of the paper coating binder class, including, for example, gum arahic, casein, hydroxyethylcellulose, and latexes (such as styrene-butadiene copolymer). If desired, oil absorbents in the form of fullers earths may be combined with the polymeric material particles to assist in retaining. in situ, the liquid droplets of chromogenic material solution to be transferred to it in datarepresenting configuration, for the purpose of preventing bleeding" of the print.

Another method for applying the chromogenic or polymeric material individually to a single sheet of paper is by immersing a sheet of paper in l-l percent, by weight, solution of the material in an evaporable solvent. Of course, this operation must be conducted individually for each reactant, because if the other reactant material were present, contact of the reactants would result in a premature coloration over the sheet area. A dried sheet with one component can then be coated with a solution of another component, the solvent of which is a nonsolvent to the already supplied component.

The polymeric material can also be dissolved in ink composition vehicles to form a printing ink" of colorless character and, thus, may be used to spot-print a proposed record sheet unit sensitized for recording, in a reactionproduced color in those spot-printed areas, by application of a solution of the chromogenic material. In the case of phenolic polymer, a printing ink may be made of up to 75 percent, by weight, of the phenolic polymeric material in a petroleumbased solvent; -the ink being built to a viscosity suitable for printing purposes. The relative amounts of reactive, markforming, components to be used in practice of this invention, are those most convenient and economical amounts consistent with adequate, desired or required visibility of the recorded data. The resolution of the recorded data is dependent on, among other things, particle or capsule size, distribution and amount of particles or capsules, liquid solvent migration, chemical reaction efiiciency, and other factors, all of which can be optimized empirically by one skilled in the art. Such factors do not determine the principle of the present invention, which invention, in part, relates to means for enabling the bringing into solution contact, by marking pressure, two normally solid, chemically reactive, components dissolved in a common liquid solvent component held isolated as liquid droplets. The isolated liquid droplets are preferably in marking-pressure-rupturable capsules having polymeric-film walls, or are isolated, as a discontinuous phase, in a continuous marking-pressure-rupturable film.

In the color system of this invention the acidic mark-forming material reacts with the novel chromogenic material to effect distinctive color formation or color change. In a multisheet system in which an acidic organic polymer is employed, it may be desirable to include other materials to supplement the polymer reactants. For example, kaolin can be added to improve the transfer of the liquid and/or the dissolved materials between the sheets. In addition, other materials such as bentonite, attapulgite, talc, feldspar, halloysite, magnesium trisilicate, silica gel, pyrophyllite, zinc sulfate, calcium sulfate, calcium citrate, calcium phosphate, calcium fluoride, barium sulfate and tannic acid can be included.

Various methods known to the prior art and others disclosed in the aforementioned abandoned application Ser. No. 392,404 in the names of Miller, et al. and in US. Pat. No. 3,455,721 issued July I5, 1969 on the application of Phillips, et. al. can be employed in compositions useful for coating mark-forming materials into supporting sheets. An example of the compositions which can be coated onto the receiving surface of an underlying sheet of a multisheet to react with a capsule coating on the underside of an overlying sheet is as follows:

Percent Coating Composition By Weight Phenolic olymer mixture 7 Paper coating Kaolin (white) 57 Calcium carbonate l2 Styrene butudiene lutex Ethylutcd slurch lt Gum uruhic 2 Tutul Having disclosed, generally, the novel chromogenic materials of this invention and preferred methods for utilizing the novel chromogenic materials, in combination with other materials, as reactive components in mark-forming record material; examples will now be disclosed wherein preparation of several of the novel chromogenic materials is described.

DESCRIPTION OF PREFERRED EMBODIMENTS EXAMPLE I Preparation of 6-diethylamino-2-nitrofluoran A reaction mixture of 3.l grams of 2-carboxy-4'- diethylamino-2'-hydroxybenzophenone, l.4 grams of pnitrophenol, and 30 milliliters of 90 percent, by weight, sulfuric acid was heated for 1 hour in a bath maintained at l45-l54 C. The reaction mixture was poured onto 300 grams of ice and made alkaline, by addition of dilute ammonium hydroxide, to a pH above 8. The chilled, alkaline, system was extracted three times with I00 milliliter-volumes of benzene to remove the product of reaction; and then the benzene extract was washed 3 times with l00 millilitervolumes of 10 percent, by weight, aqueous sodium hydroxide solution followed by repeated washes with distilled water until the wash water was no longer alkaline. The water-washed benzene extract was then evaporated to dryness to obtain about 1.2 grams of crude reaction product. The crude product was chromatographically purified over activated alumina and then recrystallized from benzene-petroleum ether. lt exhibited a melting point of l92-l93 C. A benzene solution of the purified product imparted an orange color to paper coated with a mixture of kaolin and phenolic polymer.

EXAMPLE 2 Preparation of 2'-amino-6-diethylaminofluoran A suspension was prepared by adding 0.4 grams of 6- diethylamino-2-nitrofluoran, the product of example 1, above, to a reducing solution comprising l.0 gram of stannous chloride dihydrate, 4.5 milliliters of hydrochloric acid (having a specific gravity of about 1.15), and 1.5 milliliters of water. The suspension was warmed and agitated until a solution was formed. The solution was cooled to about room temperature, was diluted with about 40 milliliters of water and the pH was adjusted to about 12 using a 10 percent, by weight, aqueous solution of sodium hydroxide in order to precipitate the reaction product. The precipitate was extracted by two 50-milliliter volumes of benzene and the benzene extract was washed repeatedly with distilled water until the wash water was no longer alkaline. The water-washed benzene extract was concentrated to about 6-7 milliliters. On standing, the reaction product separated from solution, was removed by filtration, and was washed with 2-3 milliliters of benzene. The product of this example weighed 0.21 grams and exhibited a melting point of 2l32l5 C. A benzene solution of the product imparted a purple color to paper coated with a mixture of kaolin and phenolic polymer.

EXAMPLE 3-carboxy--hydroxybenzophenone, l24Suspending Preparation of 6'-diethylamino-3 '-methyl-2 '-nitrofluoran A reaction mixture of 14.! grams of 2-carboxy-4'- diethylamino-2'-hydroxybenzophenone, 6.9 grams of 3- methyl-4-nitrophenol and milliliters of 90 percent, by weight, sulfuric acid were heated for 2 hours in a bath maintained at l24128 C. The reaction mixture was poured onto 700 grams of ice and made alkaline by addition of concentrated ammonium hydroxide to a pH of about 9. The reaction product precipitated and was removed by filtration. The thusremoved reaction product was washed twice by suspending it in 500 milliliter portions of water, stirring the suspension for one-half hour and filtering. The resulting, water-washed, crude product of reaction was black in color and weighed about l7.7 grams. The crude product was repeatedly extracted using small volumes of warmed ethyl acetate until a new volume of extract imparted only a faint color to paper coated with a mixture of kaolin and phenolic polymer. The ethyl acetate extract solution was concentrated. by evaporation, to a volume of about I50 of Cooling of the concentrated solution caused precipitation and about l2.4 grams of the precipitate was isolated and purified as in previous examples. The purified product was pale yellow and had a melting point of 266268. A benzene solution of the purified product imparted an orange color to paper coated with a mixture of kaolin and phenolic polymer.

EXAMPLE 4 Preparation of 2-amino-6'diethylamino-3-methylfluoran A suspension was prepared by adding 8.6 grams of 6'- diethylamino-3'-methyl-2'-nitrofluoran, the product of example 3, above, to a reducing solution comprising 22.5 grams of stannous chloride dihydrate, 100 milliliters of hydrochloric acid (having a specific gravity of about 1.15), 34 milliliters of water and 70 milliliters of ethanol. The system was warmed, cooled, diluted, and the pH was adjusted to about l2, all according to the procedure of example 2. The suspension was extracted several times by benzene and the extract was washed with aqueous sodium hydroxide solution and water. The washed extract was concentrated by evaporation and, on standing, the reaction product separated from solution, was removed by filtration, and was purified by recrystallization from benzene. The purified product exhibited a double melting point, i.e., on heating, it melted at about 140 C., resolidified and melted again at about l83l85 C. A benzene solution of the product imparted a purple color to paper coated with a mixture of kaolin and phenolic polymer.

EXAMPLE 5 Preparation of 6-diethylamino-2'-methyl-4'-nitrofiuoran This example was conducted according to the procedure of example I except that 4-methyl-2-nitrophenol was substituted for the p-nitrophenol therein. A benzene solution of the reaction product imparted a reddish-orange color to paper coated with a mixture of kaolin and phenolic polymer.

EXAMPLE 6 Preparation of 4-amino-6-diethylamino-2'-methylfluoran 6'-diethylamino-2'-methyl-4'-nitrofluoran from example 5, above, was reduced with stannous chloride according to the procedure of example 2, above. The reaction product exhibited a double melting point, i.e., on heating, it melted at about 135 C., resolidified, and melted again at about 230 C. A benzene solution of the product imparted on orange color to paper coated with a mixture of kaolin and phenolic polymer.

EXAMPLE 7 Preparation of 2-chloro-6'-diethylamino-3'-methyl-5(or 6)- nitrofluoran Five grams of m-diethylaminophenol, 5.8 grams of 4- nitrophthalic anhydride, and 100 milliliters of benzene were refluxed together for about three hours. The mixture was,

cooled and extracted twice with 100 milliliter-volumes of.5 percent by weight, aqueous sodium carbonate solution. Dilute, aqueous, hydrochloric acid was added, dropwise, to the sodium carbonate-extract solution to precipitate the reaction product. The precipitate thrown down between pH 6 and pH 2 was collected for use as an intermediate to the desired product of this example. Said intermediate is 2-carboxy-4'- diethylamino-2'-hydroxy-4(or 5)-nitrobenzophenone and 4.3 grams of It were obtained. The intermediate was condensed with 4-ch|oro-3-methylphenol in percent, by weight, sult'uric acid ut l05 C, for about 3 hours and the reaction product was isolated by the technique described in example I, above. A benzene solution of the product imparted a red color to paper coated with a mixture of kaolin and phenolic polymer.

EXAMPLE 8 wherein:

one of R, R R and R represents nitro-radicals and the remaining others of R, R,, R and R represent radicals selected from the group consisting of hydrogen, halogen, phenyl and alkyl radicals having less than five carbon atoms; and

R, represents alkyl radicals having less than five carbon atoms.

2. The chromogenic compound of claim 1 wherein R is a nitro-radical, R, is an ethyl radical, and R, R,, and R are hydrogen radicals, said compound being 6diethylamino-2'- nitrofluoran.

3. The chromogenic compound of claim 1 wherein R is a nitro-radical, R is a methyl radical, R, is an ethyl radical, and R and R are hydrogen radicals, said compound being 6- diethylamino-Z-methyl-2'-nitrofluoran.

4. The chromogenic compound of claim 1 wherein R is a methyl radical, R is a nitro-radical, R, is an ethyl radical, and R and R are hydrogen radicals, said compound being 6'- diethylamino-Z-methyl-4-nitrofluoran.

5. The chromogenic compound of claim 1 wherein R is a chloro-radical, R is a methyl radical, R, is an ethyl radical, R is a nitro-radical, and R is a hydrogen radical, said compound being selected from the group consisting of 2'-chloro-6'- diethylamino-3-methyl-5-nitrofluoran and 2-chloro-6'- diethylamino-3'-methyl-6-nitrofluoran.

6. A chromogenic compound selected from the group consisting of 5-amino-2'-chloro-6'-diethylamino-3'-methylfluoran and 6amino2'-chloro-6'-diethylamino-3-methylfluoran.

a: a t =r 

2. The chromogenic compound of claim 1 wherein R2 is a nitro-radical, R4 is an ethyl radical, and R, R1, and R3 are hydrogen radicals, said compound being 6''-diethylamino-2''-nitrofluoran.
 3. The chromogenic compound of claim 1 wherein R2 is a nitro-radical, R1 is a methyl radical, R4 is an ethyl radical, and R and R3 are hydrogen radicals, said compound being 6''-diethylamino-2''-methyl-2''-nitrofluoran.
 4. The chromogenic compound of claim 1 wherein R2 is a methyl radical, R is a nitro-radical, R4 is an ethyl radical, and R1 and R3 are hydrogen radicals, said compound being 6''-diethylamino-2''-methyl-4''-nitrofluoran.
 5. The chromogenic compound of claim 1 wherein R2 is a chloro-radical, R1 is a methyl radical, R4 is an ethyl radical, R3 is a nitro-radical, and R is a hydrogen radical, said compound being selected from the group consisting of 2''-chloro-6''-diethylamino-3''-methyl-5-nitrofluoran and 2''-chloro-6''-diethylamino-3''-methyl-6-nitrofluoran.
 6. A chromogenic compound selected from the group consisting of 5-amino-2''-chloro-6''-diethylamino-3''-methylfluoran and 6amino-2''-chloro-6''-diethylamino-3''-methylfluoran. 